Glycols such as 1,4-butanediol and 1,6-hexanediol are useful as monomers in a number of polymers including, thermoplastics such as the polyester thermoplastics and polyether thermoplastics. Examples of such thermoplastics include poly(1,4-butylene terphthalate) resin block copolymers containing blocks of poly(butyl ether) and aliphatic polyesters such as poly(hexylene adipate).
The glycol products also find wide application in pharmaceutical and cosmetic uses where the degree of purity and color is of prime consideration. A common method for preparing glycols has involved the hydrogenation of a butynediol in the presence of a nickel/copper/manganese catalyst at a pressure between about 300 and about 2000. However, this process results in a product significantly contaminated with a aldehydes, alkene diols and color forming impurities which are particularly objectionable when the product is employed as an adduct in cosmetic and pharmaceutical formulations. Alkene diols and acid aldehydes are particularly troublesome because of their well known skin irritating properties. Also, the presence of low boiling aldehydes lowers the stability of the product on storage. Accordingly, improved methods for the preparation of glycols in a more purified state has been the subject of current research projects. Many catalyst combinations, such as those discussed in the following patents, have been employed to achieve this end.
Of particular interest in the background of the present invention is the catalytic conversion 1,4-butynediol to 1,4-butanediol as described in U.S. Pat. No. 3,759,845 entitled CATALYST FOR PREPARING 1,4-BUTANEDIOL. This patent discloses a nickel/copper/manganese on alumina hydrogenation catalyst which has improved stability and longer life than catalysts previously employed in similar reactions.
Another process for the conversion of 1,4-butynediol to 1,4-butanediol is described in U.S. Patent 3,499,445 to Wetherill. The process described therein comprises a partial hydrogenation of a pretreated aqueous solution of 1,4-butynediol of about 35% to 40% concentration from which formaldehyde has been removed by the procedure described in U.S. Pat. No. 2,993,708, at a pH of 6.5 about 7.5. The solution is fed to a low pressure reactor containing a Raney-type nickel catalyst of the type described in U.S. Patent 1,638,190, which is readily prepared by treating an aluminum alloy with caustic soda to dissolve out the aluminum and leave the nickel in a highly divided form. After the 1,4-butynediol solution is charged, the reactor is maintained at a temperature from about 50.degree. to about 150.degree. C. and under a hydrogen pressure of 200 and 300 psig. until the desired partial hydrogenation of the 1,4-butynediol is achieved as determined by the cessation of hydrogen absorption.
The reaction mixture is allowed to settle and the partially hydrogenated product is separated from the catalyst and charged to an intermediate storage zone for pumping into the subsequent high pressure portion of the process. From the intermediate storage zone, the partially hydrogenated solution is charged to a high pressure reactor maintained at about 2,000 to about 3,000 psig at a temperature of about 120.degree. to 140.degree. C. A stream of hydrogen is simultaneously charged under pressure to the reactor. The reactor is filled with a fixed bed of catalyst comprising about 12 to 17% by weight of nickel, 4 to 8% by weight of copper and 0.3 to 1.0% by weight of manganese supported on a silica gel carrier.
The hydrogenated liquid product is separated from the residual hydrogen which is recycled together with make-up hydrogen and returned to the reactor. The separated liquid product is then cooled to about room temperature and charged to a storage tank. The product so obtained can then be subjected to distillation to recover 1,4-butanediol product. It has been found, however, that the silica gel carriers employed as the catalyst supports in the high pressure reactors of the above-described processes physically degrade under the process conditions resulting in the production of fines which cause pressure fluctuations in the high pressure reactor. These pressure fluctuations result in intermittent shut-downs, high catalyst replacement costs and consequent loss of production.
Accordingly, it is an object of the present invention to provide an improved hydrogenation catalyst system which overcomes the deficiencies of the above hydrogenation processes while exhibiting longer life and higher activity resulting in longer productivity and improved process economics.
Another object of this invention is to provide an improved catalyst for the hydrogenation of compounds containing carbon to carbon unsaturation or a carbonyl group.
It is another object of the present invention to provide an improved hydrogenation process for the conversion of 1,4-butynediol to 1,4-butanediol in high yields and selectivity.
It is another object of the present invention to provide a highly active hydrogenation catalyst which can be prepared by an economical and commercially feasible process.
These and other objects of the invention will become apparent from the following description and disclosure.